Devices and methods for the treatment of spinal disorders

ABSTRACT

Devices and methods for treating a damaged intervertebral disc to reduce or eliminate associated back pain. Dynamic bias devices and reinforcement devices are disclosed, which may be used individually or in combination, to eliminate nerve impingement associated with the damaged disc, and/or to reinforce the damaged disc, while permitting relative movement of the vertebrae adjacent the damaged disc.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/967,042 filed Oct. 15,2004, now pending, which is a continuation of application Ser. No.10/093,990 filed Mar. 7, 2002, now U.S. Pat. No. 6,835,205, issued Dec.28, 2004, which is a continuation of application Ser. No. 09/542,972filed Apr. 4, 2000, now U.S. Pat. No. 6,402,750, issued Jun. 11, 2002,the entireties of all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to spinal implants.Specifically, the present invention relates to implantable devices andmethods for the treatment of spinal disorders associated with theintervertebral disc.

BACKGROUND OF THE INVENTION

Back pain is one of the most common and often debilitating conditionsaffecting millions of people in all walks of life. Today, it isestimated that over ten million people in the United States alone sufferfrom persistent back pain. Approximately half of those suffering frompersistent back pain are afflicted with chronic disabling pain, whichseriously compromises a person's quality of life and is the second mostcommon cause of worker absenteeism. Further, the cost of treatingchronic back pain is very high, even though the majority of sufferers donot receive treatment due to health risks, limited treatment options andinadequate therapeutic results. Thus, chronic back pain has asignificantly adverse effect on a person's quality of life, onindustrial productivity, and on heath care expenditures.

Some forms of back pain are not chronic and may be simply treated byrest, posture adjustments and painkillers. For example, some forms oflower back pain (LBP) are very common and may be caused by unusualexertion or injury. Unusual exertion such has heavy lifting or strenuousexercise may result in back strain such as a pulled muscle, sprainedmuscle, sprained ligament, muscle spasm, or a combination thereof. Aninjury caused by falling down or a blow to the back may cause bruising.These forms of back pain are typically non-chronic and may beself-treated and cured in a few days or weeks.

Other types of non-chronic back pain may be treated by improvements inphysical condition, posture and/or work conditions. For example, beingpregnant, obese or otherwise significantly overweight may cause LBP. Amattress that does not provide adequate support may cause back pain inthe morning. Working in an environment lacking good ergonomic design mayalso cause back pain. In these instances, the back pain may be cured byeliminating the culprit cause. Whether it is excess body weight, a badmattress, or a bad office chair, these forms of back pain are readilytreated.

However, some forms of back pain are chronic and are the result ofspinal disorders which are not readily treated. Such spinal disordersmay cause severe back pain, the origin of which may or may not becertain. A prevalent clinical theory is that pain arises from physicalimpingement of the nerve roots or the spinal cord. Such nerveimpingement may have of a number of different causes, but generallyresults from either a disc protrusion or from narrowing of theintervertebral foramina which surround the nerve roots. Another clinicaltheory is that damage to the disc, either from injury, degradation orotherwise, causes physical impingement of the disc nerves, which areprimarily disposed about the periphery of the annulus, but may grow intofissures of a damaged disc.

Disc protrusions may be caused by a physical injury to the disc or bynatural degradation of the disc such as by degenerative disc disease(DDD). Physical injury may cause damage to the annulus fibrosus whichallows a portion of the disc, such as the nucleus pulposus, to protrudefrom the normal disc space. DDD may cause the entire disc to degenerateto such a degree that the annulus fibrosus bulges outward, delaminatesor otherwise separates such that a portion of the disc protrudes fromthe normal disc space. In either case, the disc protrusion may impingeon a spinal nerve root causing severe pain. Impingement on the nerveroot may also be caused by conditions unrelated to the disc such as by aspinal tumor or spinal stenosis (abnormal bone growth), but discprotrusions are the most common cause. Depending on the cause and natureof the disc protrusion, the condition may be referred to as a discstenosis, a disc bulge, a herniated disc, a slipped disc, a prolapseddisc or, if the protrusion separates from the disc, a sequestered disc.

Nerve root impingement most often occurs in the lumbar region of thespinal column since the lumbar discs bear significant vertical loadsrelative to discs in other regions of the spine. In addition, discprotrusions in the lumbar region typically occur posteriorly because theannulus fibrosus is thinner on the posterior side than on the anteriorside and because normal posture places more compression on the posteriorside. Posterior protrusions are particularly problematic since the nerveroots are posteriorly positioned relative to the intervertebral discs.When a posterior disc protrusion presses against a nerve root, the painis often severe and radiating, and may be aggravated by such subtlemovements as coughing, bending over, or remaining in a sitting positionfor an extended period of time.

A common treatment for disc protrusion is discectomy, which is aprocedure wherein the protruding portion of the disc is surgicallyremoved. However, discectomy procedures have an inherent risk since theportion of the disc to be removed is immediately adjacent the nerve rootand any damage to the nerve root is clearly undesirable. Furthermore,discectomy procedures are not always successful long term because scartissue may form and/or additional disc material may subsequentlyprotrude from the disc space as the disc deteriorates further. Therecurrence of a disc protrusion may necessitate a repeat discectomyprocedure, along with its inherent clinical risks and less than perfectlong term success rate. Thus, a discectomy procedure, at least as astand-alone procedure, is clearly not an optimal solution.

Discectomy is also not a viable solution for DDD when no disc protrusionis involved. As mentioned above, DDD causes the entire disc todegenerate, narrowing of the intervertebral space, and shifting of theload to the facet joints. If the facet joints carry a substantial load,the joints may degrade over time and be a different cause of back pain.Furthermore, the narrowed disc space can result in the intervertebralforamina surrounding the nerve roots to directly impinge on one or morenerve roots. Such nerve impingement is very painful and cannot becorrected by a discectomy procedure.

As a result, spinal fusion, particularly with the assistance ofinterbody fusion cages, has become a preferred secondary procedure, andin some instances, a preferred primary procedure. Spinal fusion involvespermanently fusing or fixing adjacent vertebrae. Hardware in the form ofbars, plates, screws and cages may be utilized in combination with bonegraft material to fuse adjacent vertebrae. Spinal fusion may beperformed as a stand-alone procedure or may be performed in combinationwith a discectomy procedure. By placing the adjacent vertebrae in theirnominal position and fixing them in place, relative movement therebetween may be significantly reduced and the disc space may be restoredto its normal condition. Thus, theoretically, aggravation caused byrelative movement between adjacent vertebrae (and thus impingement onthe nerve root by a disc protrusion and/or impingement from bone may bereduced if not eliminated.

However, the success rate of spinal fusion procedures is certainly lessthan perfect for a number of different reasons, none of which are wellunderstood. In addition, even if spinal fusion procedures are initiallysuccessful, they may cause accelerated degeneration of adjacent discssince the adjacent discs must accommodate a greater degree of motion.The degeneration of adjacent discs simply leads to the same problem at adifferent anatomical location, which is clearly not an optimal solution.Furthermore, spinal fusion procedures are invasive to the disc, risknerve damage and, depending on the procedural approach, eithertechnically complicated (endoscopic anterior approach), invasive to thebowel (surgical anterior approach), or invasive to the musculature ofthe back (surgical posterior approach).

Another procedure that has been less than clinically successful is totaldisc replacement with a prosthetic disc. This procedure is also veryinvasive to the disc and, depending on the procedural approach, eitherinvasive to the bowel (surgical anterior approach) or invasive to themusculature of the back (surgical posterior approach). In addition, theprocedure may actually complicate matters by creating instability in thespine, and the long term mechanical reliability of prosthetic discs hasyet to be demonstrated.

Many other medical procedures have been proposed to solve the problemsassociated with disc protrusions. However, many of the proposedprocedures have not been clinically proven and some of the allegedlybeneficial procedures have controversial clinical data. From theforegoing, it should be apparent that there is a substantial need forimprovements in the treatment of spinal disorders, particularly in thetreatment of nerve impingement as the result of damage to the disc,whether by injury, degradation, or the like.

SUMMARY OF THE INVENTION

The present invention addresses this need by providing improved devicesand methods for the treatment of spinal disorders. As used herein, theterm spinal disorder generally refers to a degradation in spinalcondition as the result of injury, aging or the like, as opposed to aspinal deformity resulting from growth defects. The improved devices andmethods of the present invention specifically address nerve impingementas the result of damage to the disc, particularly in the lumbar region,but may have other significant applications not specifically mentionedherein. For purposes of illustration only, and without limitation, thepresent invention is discussed in detail with reference to the treatmentof damaged discs in the lumbar region of the adult human spinal column.

As will become apparent from the following description, the improveddevices and methods of the present invention reduce if not eliminateback pain while maintaining near normal anatomical motion. Specifically,the present invention provides dynamic bias devices and reinforcementdevices, which may be used individually or in combination, to eliminatenerve impingement associated with a damaged disc, and/or to reinforce adamaged disc, while permitting relative movement of the vertebraeadjacent the damaged disc. The devices of the present invention areparticularly well suited for minimally invasive methods of implantation.

The dynamic bias devices of the present invention basically apply a biasforce to adjacent vertebrae on either side of a damaged disc, whilepermitting relative movement of the vertebrae. By applying a bias force,disc height may be restored, thereby reducing nerve impingement.Specifically, by restoring disc height, the dynamic bias devices of thepresent invention: retract disc protrusions into the normal disc spacethereby reducing nerve impingement by the protrusions; reduce the loadcarried by the facet joints thereby eliminating nerve impingementoriginating at the joint; restore intervertebral spacing therebyeliminating nerve impingement by the intervertebral foramina; and reducepressure on portions of the annulus thereby alleviating nerveimpingement in disc fissures.

The reinforcement devices of the present invention basically reinforce adamaged disc, restore disc height and/or bear some or all of the loadnormally carried by a healthy disc, thereby reducing nerve impingement.Some embodiments of the reinforcement members of the present inventionhave a relatively small profile when implanted, but are very rigid, andthus serve to reinforce the disc, particularly the annulus. Byreinforcing the disc, and particularly the annulus, disc protrusions mayreduced or prevented, thereby eliminating nerve impingement by theprotrusions. Other embodiments have a relatively large profile whenimplanted, and thus serve to increase disc height and/or to bear load.By increasing disc height, the advantages discussed previously may beobtained. By bearing some of the load normally carried by a healthydisc, the load may be redistributed as needed, such as when a dynamicbias device is used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate left lateral and posterior views,respectively, of a portion of the adult human vertebral (spinal) column;

FIG. 2A illustrates a left lateral view of an intervertebral discdisposed between adjacent vertebrae, wherein the disc is partiallyprotruding from the normal disc space and the disc height is reduced;

FIG. 2B illustrates a left lateral view of an intervertebral discdisposed between adjacent vertebrae as in FIG. 2A, wherein dynamic biasdevices and reinforcement devices of the present invention, which areillustrated schematically, restore normal disc height and eliminate thedisc protrusion;

FIGS. 3A-3C schematically illustrate a dynamic bias device 100 inaccordance with the present invention;

FIGS. 4A-4B schematically illustrate left lateral and posterior views,respectively, of dynamic bias devices of the present invention mountedto adjacent vertebrae equidistant from the median plane;

FIGS. 5A-5B schematically illustrate left lateral and posterior views,respectively, of a dynamic bias device of the present invention mountedto adjacent vertebrae in the median plane;

FIGS. 6A-6B illustrate end and exploded views, respectively, of abushing in accordance with a first embodiment of the present invention;

FIG. 6C illustrates a posterior view of the bushing shown in FIGS. 6A-6Bmounted to a spinous process;

FIG. 6D illustrates a posterior view of the spinous process shown inFIG. 6C, detailing the counter-bore;

FIGS. 7A-7B illustrate end and exploded views, respectively, of abushing in accordance with a second embodiment of the present invention;

FIGS. 8A-8B illustrate end and exploded views, respectively, of abushing in accordance with a third embodiment of the present invention;

FIGS. 9A-9B illustrate end and exploded views, respectively, of abushing in accordance with a fourth embodiment of the present invention;

FIG. 10A illustrates a side view of a dynamic bias device in accordancewith a first embodiment of the present invention;

FIG. 10B illustrates a side view of the dynamic bias device shown inFIG. 10A subjected to a compression load;

FIG. 10C illustrates a cross-sectional view of the dynamic bias deviceshown in FIG. 1A;

FIG. 11A illustrates a cross-sectional view of a dynamic bias device inaccordance with a second embodiment of the present invention;

FIG. 11B illustrates a cross-sectional view of a dynamic bias device inaccordance with a third embodiment of the present invention;

FIGS. 12A-12B illustrate rear and side views, respectively, of a dynamicbias device in accordance with a fourth embodiment of the presentinvention;

FIG. 12C illustrates the dynamic bias device shown in FIGS. 12A-12Bsubjected to a compression load;

FIG. 13A illustrates a side view of a dynamic bias device in accordancewith a fifth embodiment of the present invention;

FIG. 13B illustrates a side or rear view of a dynamic bias device inaccordance with a sixth embodiment of the present invention;

FIG. 13C illustrates a rear view of a dynamic bias device in accordancewith a seventh embodiment of the present invention;

FIGS. 14A-14D illustrate tools of the present invention for implantingthe reinforcement members;

FIGS. 15A-15J illustrate steps for implanting a self-expandingreinforcement member;

FIGS. 15K-15L illustrate steps for implanting an inflatablereinforcement member;

FIGS. 15M-15R illustrate steps for implanting reinforcement bars; and

FIG. 16 illustrates a bias force v. displacement curve for the dynamicbias device.

DETAILED DESCRIPTION

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

With reference to FIGS. 1A and 1B, the lower portion of an adult humanvertebral column 10 is illustrated in left lateral and posterior views,respectively. The upper portion of the vertebral column 10 includes thethoracic region and the cervical region, which are not shown forpurposes of simplified illustration only. The lower portion of thevertebral column 10 includes the lumbar region 12, the sacrum 14 and thecoccyx 16. The sacrum 14 and the coccyx 16 are sometimes collectivelyreferred to as the pelvic curvature.

The vertebral column 10 includes an axis of curvature 60 which generallyforms a double-S shape when viewed laterally. The vertebral column 10also includes a median plane 70 which is a sagittal plane bisecting thevertebral column 10 into symmetrical left lateral and right lateralportions. In posterior views, the median plane 70 appears as a line.

The lumbar region 12 of the vertebral column 10 includes five (5)vertebrae 20 (labeled L1, L2, L3, L4 and L5) separated by intervertebraldiscs 50. The sacrum 14, which includes five (5) fused vertebrae 30(superior vertebra 30 labeled S1), is separated by a single disc 50 fromthe coccyx 16, which includes four (4) fused vertebrae 40. Although notlabeled, the intervertebral discs 50 may be referenced by theirrespective adjacent vertebrae. For example, the disc 50 between the L4and L5 lumbar vertebrae 20 may be referred to as the L4L5 disc.Similarly, the disc 50 between the L5 lumbar vertebra 20 and the S1sacral vertebra 30 may be referred to as the L5S1 disc.

Although each vertebra 20/30/40 is a unique and irregular bonestructure, the vertebrae 20 of the lumbar region 12 (in addition to thethoracic and cervical regions) have common structures. Each vertebra 20of the lumbar region 12 generally includes a body portion 21 and avertebral arch portion 22/23 which encloses the vertebral foramen (notvisible) in which the spinal cord is disposed. The vertebral arch 22/23includes two pedicles 22 and two laminae 23. A spinous process 24extends posteriorly from the juncture of the two laminae 23, and twotransverse processes 25 extend laterally from each lamina 23. Fourarticular processes 26/27 extend inferiorly 26 and superiorly 27 fromthe laminae 23. The inferior articular process 26 rests in the superiorarticular process 27 of the adjacent vertebra to form a facet joint 28.

The five (5) vertebrae 30 of the sacrum 14 are fused together to form asingle rigid structure. The sacrum 14 includes a median sacral crest 31which roughly corresponds to the spinous processes of the vertebrae 30,and two intermediate sacral crests 32 which roughly correspond to thearticular processes of the vertebrae 30. The sacral laminae 33 aredisposed between the median 31 and intermediate 32 sacral crests. Twolateral sacral crests 34 are disposed on either side of the sacralforaminae 35. The sacrum 14 also includes a pair of sacral wings 36which define auricular surfaces 39. The superior (S1) sacral vertebra 30includes two superior articular processes 37 which engage the inferiorarticular processes 26 of the L5 lumber vertebra 20 to form a facetjoint, and the base 38 of the superior sacral vertebra S1 is joined tothe L5S1 disc 50.

Each intervertebral disc 50 includes an annulus fibrosus 52 surroundinga nucleus pulposus 54, which are more clearly visible in FIG. 15A. Theposterior annulus 52 is generally thinner than the anterior annulus 52,which may account for the higher incidence of posterior discprotrusions. As used herein, a disc protrusion generically refers to anyportion of the disc that protrudes from the normal disc space. Commonclinical conditions that may be characterized as a disc protrusioninclude a disc stenosis, a disc bulge, a herniated or sequestered disc,a slipped disc, and a prolapsed disc. Generally, a disc protrusionresults in a decrease in disc height proportional to the volume of theprotrusion. A degenerative disc may sometimes only involve the loss ofdisc height, and may or may not involve any significant protrusion.However, both degenerative discs and a disc protrusions usually involvesome loss in disc height.

A common theory is that each intervertebral disc 50 forms one supportpoint and the facet joints form two support points of what may becharacterized as a three point support structure between adjacentvertebrae. However, in the lumbar region 12, the facet joints 28 aresubstantially vertical, leaving the disc 50 to carry the vast majorityof the load. As between the annulus fibrosus 52 and the nucleus pulposus54 of the disc 50, it is commonly believed that the nucleus 54 bears themajority of the load. This belief is based on the theory that the disc50 behaves much like a balloon or tire, wherein the annulus 22 merelyserves to contain the pressurized nucleus 54, and the nucleus 54 bearsall the load.

However, this theory is questionable since the annulus fibrosus 52comprises 60% of the total disc 50 cross-section, and the nucleuspulposus 54 only comprises 40% of the total disc 50 cross-section. Inaddition, the annulus fibrosus 52 is made of 40-60% organized collagenin the form of a laminated structure, whereas the nucleus pulposus 54 ismade of 18-30% collagen in the form of a relatively homogenous gel. Itseems a more plausible theory is that the annulus fibrosus 52 is theprimary load bearing portion of the disc 50.

With reference to FIG. 2A, a left lateral view of an intervertebral disc50 disposed between adjacent vertebrae 20 _(S) (superior) and 20 _(I)(inferior) is illustrated, wherein the disc 50 is partially protruding56 from the normal disc space and the disc height is reduced. Althoughthe disc 50 is shown to include a protrusion 56, the reduction in discheight may or may not be accompanied with a protrusion 56 as discussedpreviously. For example, if the disc 50 is degenerated, the disc heightmay be reduced with or without a corresponding protrusion 56.

It should be understood that the vertebrae shown in FIGS. 2A and 2Bgenerically refer to any two adjacent vertebrae or any series ofadjacent vertebrae, and that lumbar vertebrae 20 _(S) and 20 _(I) arespecifically shown for purposes of illustration only. This genericmethod of illustrating vertebrae also applies to the remainder of theFigures.

With reference to FIG. 2B, a left lateral view of the intervertebraldisc 50 disposed between adjacent vertebrae 20 _(S) and 20 _(I) isillustrated as in FIG. 2A. However, in this Figure, devices 100 and 200of the present invention, which are illustrated schematically, eliminatethe disc protrusion 56 and restore normal disc height. Specifically, oneor more dynamic bias devices 100 and one or more reinforcement members200 are utilized, either in combination or individually.

The dynamic bias device 100 restores disc height and, by conservation ofdisc volume, retracts the protrusion into the normal disc space therebyreducing nerve impingement by the protrusion. Restoring disc height alsoreduces the load carried by the facet joints thereby eliminating nerveimpingement originating at the joint, restores intervertebral spacingthereby eliminating nerve impingement by the intervertebral foramina,and reduces pressure on portions of the annulus thereby alleviatingnerve impingement in disc fissures.

The dynamic bias device 100 basically applies a bias force to theadjacent vertebrae 20 _(S) and 20 _(I) to which it is connected, butallows relative movement of the vertebrae 20 _(S) and 20 _(I). Thedynamic bias device 100 is conceptually similar to a spring attached tothe adjacent vertebrae 20 _(S) and 20 _(I). The dynamic bias device 100applies a bias force (usually repulsive) between the vertebrae 20 _(S)and 20 _(I) when the disc height is normal or less than normal. The biasforce is preferably set such that the disc height is normal with normalposture and loading, and increases with posterior flexure and/or addedvertical load. The details of the design and use of the dynamic biasdevice 100 will be discussed in greater detail hereinafter, particularlywith reference to FIGS. 3A-3C, 4A-4B, 5A-5B, 10A-10C, 11A-11B, 12A-12C,and 13A-13C.

Because most protrusions 56 are posterior, the dynamic bias device 100is preferably mounted posterior to the axis of curvature 60. Locatingthe dynamic bias device 100 posterior to the axis of curvature 60 shiftsthe load carried by the disc 50 from the posterior portion of the discto the anterior portion of the disc 50. Locating the dynamic bias device100 posterior to the axis of curvature 60 also reduces the load carriedby the facet joints. Preferably, the dynamic bias device 100 applies asubstantially vertical bias force, with the direction independent ofdisplacement.

Because more load will be shifted to the anterior portion of the disc 50with a posterior mounted dynamic bias device 100, reinforcement members200 may be placed in the anterior annulus 52, to effectively bolster theanterior portion of the disc. The reinforcement members 200 may be usedto reinforce the disc, restore disc height and/or bear the load normallycarried by annulus. The reinforcement members 200 are relatively rigidand thus serve to reinforce the disc 50 where inserted. In addition, thereinforcement members 200 may have a relatively large profile whenimplanted and thus increase disc height. The reinforcement members 200are particularly beneficial if the disc 50 is degenerated, or if thedisc 50 will likely become degenerated with the change in loaddistribution. The details of the design and use of the reinforcementmembers 200 will be discussed in greater detail hereinafter,particularly with reference to FIGS. 14A-14D and 15A-15R.

As mentioned previously, one or more dynamic bias devices 100 and one ormore reinforcement members 200 may be utilized, either alone or incombination. Specifically: one or more dynamic bias devices 100 may beused alone; one or more spacer devices 200 may be used alone; and one ormore dynamic bias devices 100 and one or more reinforcement members 200may be used in combination. If a combination of devices 100/200 is used,it is believed that the use of one or more posterior dynamic biasdevices 100 in combination with one or more anterior reinforcementmembers 200 is most effective in treating posterior protrusions 56,facet joint degradation, and nerve impingement by intervertebralforaminae, which are believed to be the most common culprits of chronicLBP.

As an alternative to the arrangement shown in FIG. 2B, two or moredynamic bias devices 100 may be attached to the vertebrae on oppositesides of vertebrae 20 _(S) and 20 _(I). Specifically, one or moredynamic bias devices 100 is connected to vertebra 20 _(S) and thevertebra immediately superior to vertebra 20 _(S), and one or moredynamic bias devices 100 is connected to vertebra 20 _(I) and thevertebra immediately inferior to vertebra 201. With this arrangement,the dynamic bias devices 100 are primarily applying a traction force toeffectively pull vertebrae 20 _(S) and 20 _(I) apart, therebyeliminating the disc protrusion 56 and restoring normal disc height.

With reference to FIGS. 3A-3C, the dynamic bias device 100 isschematically illustrated under conditions of no-load, compression load(L_(C)), and traction load (L_(T)), respectively. The dynamic biasdevice 100 includes a pair of attachment members 102, a bias member 104,and a housing 106. Attachment members 102 facilitate attachment of thedynamic bias device 100 to vertebrae 20 _(S) and 20 _(I), as shown inFIG. 2B. Bias member 104 functions to apply a bias force between theattachment members 102. Housing 106 functions to separate the movingportions of dynamic bias device 100 from the surrounding muscle,ligaments and other tissue when the dynamic bias device 100 isimplanted.

Attachment members 102 may comprise a wide variety of mechanicalconnection designs, and may incorporate into their design, or be used incombination with, other machine elements not specifically mentionedherein. For purposes of illustration only, the each attachment member102 is shown as loop which may be connected to the vertebrae byfasteners and bushings, specific examples of which are described indetail with reference to FIGS. 6A-6D, 7A-7B, 8A-8B and 9A-9B. Thesespecific examples are provided by way of example, not limitation. Thoseskilled in the art will recognize that the attachment members 102 maycomprise or include screws, rivets, spikes, keys, pins, cotters,splines, couplings, bushings, washers, and the like, without departingfrom the scope or spirit of the present invention.

The primary function of the attachment members 102 is to fixedly securethe ends of the bias member 104 to the vertebrae 20 _(S) and 20 _(I).Preferably, the attachment members 102 are secured to the vertebrae 20_(S) and 20 _(I) such that translational movement is minimized oreliminated, and such that rotational movement is permitted between eachattachment member 102 and each vertebrae 20 _(S) and 20 _(I). Providingattachment members 102 with these functional attributes permits thedynamic bias device 100 to effectively transmit a bias force to eachvertebrae 20 _(S) and 20 _(I), allow relative movement there between,and minimize stress on the vertebrae 20 _(S) and 20 _(I) at theattachment points.

Bias member 104 functions to apply a bias force, either attraction orrepulsion, between the attachment members 102. The bias force generallyincreases or decreases with displacement of the ends of the bias member104, as with a conventional spring. In addition, the bias force mayincrease or decrease with the time derivative of displacement (i.e.,velocity) of the ends of the bias member 104, as with a conventionaldamper or shock absorber. As shown in FIG. 3B, the bias member 104compresses in response to a compression load (L_(C)), thereby increasingor decreasing the bias force. Similarly, as shown in FIG. 3C, the biasmember 104 extends in response to a traction load (L_(T)), therebyincreasing or decreasing the bias force.

If the dynamic bias devices 100 are attached to vertebrae 20 _(S) and 20_(I) (compression embodiment), as shown in FIG. 2B, the bias force ofthe bias member 104 increases in response to a compression load (L_(C)),and decreases in response to a traction load (L_(T)). In addition, thebias member 104 normally operates in compression. Preferably, the biasforce of the bias member 104 is adjusted such that the disc is restoredto a more normal height when the dynamic bias device 100 is implanted.Because the disc height is usually initially less than normal, thedynamic bias device 100 is attached to the vertebrae with the biasmember 104 preloaded in compression or with the vertebrae 20 _(S) and 20_(I) in traction or otherwise spread apart. In this manner, for a givenposture, the disc height will be larger following implantation of thedynamic bias device 100 than prior to implantation.

If the dynamic bias devices 100 are attached to the vertebrae onopposite sides of vertebrae 20 _(S) and 20 _(I) (traction embodiment),as discussed as an alternative to the arrangement shown in FIG. 2B, thebias force of the bias member 104 decreases in response to a compressionload (L_(C)), and increases in response to a traction load (L_(T)). Withthis latter arrangement, the bias member 104 normally operates intension. Because the bias member 104 normally operates in tension withthis arrangement, the bias member 104 may simply comprise a member thatis rigid or semi-rigid in tension, such as a cable. Also with thisarrangement, the bias force of the bias member 104 is adjusted such thatthe disc is restored to a more normal height when the dynamic biasdevice 100 is implanted. Further with this arrangement, because the discheight is usually initially less than normal, the dynamic bias device100 is attached to the vertebrae with the bias member 104 preloaded intension or with the vertebrae 20 _(S) and 20 _(I) in traction orotherwise spread apart.

With either arrangement, the dynamic bias device 100 preferably operateswith substantially linear displacement substantially parallel to theaxis of curvature 60. However, the amount of displacement will be evenlyshared between the dynamic bias devices 100 in the traction embodiment,whereas the compression embodiment requires the full displacement to beassumed by each dynamic bias device 100. The following ranges ofdisplacement are given with reference to the compression embodiment.When mounted near the posterior portion of adjacent spinous processes,the dynamic bias device 100 may have a total (i.e., maximum)displacement preferably in the range of 1.0 to 3.0 cm to accommodatefull posterior to anterior flexure in the L5-S1 region, 0.5 to 1.5 cm toaccommodate full posterior to anterior flexure in the L4-L5 region, and0.25 to 1.0 cm to accommodate full posterior to anterior flexure in theL1-L4 region.

Within these ranges of displacement, it is preferable that bias member104 operate within its elastic limit, as dictated by the chosen materialand geometry of the bias member 104. In addition, because the biasmember preferably should be able to withstand 1.0 to 10 million fatiguecycles, it is preferable that bias member 104 operate within its fatiguelimit, as dictated by the chosen material and geometry, for the fullrange of displacement.

As mentioned previously, the bias force may generally increase ordecrease with displacement of the ends of the bias member 104, as with aconventional spring. In this situation, the bias force (F_(B)) isgenerally governed by Hooke's Law where F_(B)=KΔX, wherein F_(B) islinearly proportional to the displacement (ΔX) as dictated by the springconstant (K) of the bias member 104. Also as mentioned previously, thebias force may increase or decrease with the time derivative ofdisplacement (i.e., velocity) of the ends of the bias member 104, aswith a conventional damper or shock absorber. In this situation, thebias force (F_(B)) is generally linearly proportional to the derivativeof displacement (ΔX/ΔT) as dictated by the damper constant (P) of thebias member 104. Preferably, the bias force F_(B) of the bias member 104is adjusted such that the disc is restored to a more normal height whenthe dynamic bias device 100 is implanted. The bias force F_(B) may beadjusted by selecting the spring constant (K) and/or damper constant (P)of the bias member 104 and by pre-loading (compressing) the bias member104 an initial displacement ΔX_(i).

The necessary bias force F_(B) may be roughly calculated as a functionof body weight (BW), the distance of the mounted dynamic bias device 100from the axis of curvature 60, and the mechanical properties of thesurrounding tissues (muscle tissue, connective tissue, joints). Thenormal net load carried by the lumbar region 12 is roughly 30% BW whenlaying down, 140% BW when standing, 185% BW when sitting, 215% BW whenbending forward, and 250% BW when slouching.

With reference to FIG. 16, a bias force versus attachment pointdisplacement curve for the dynamic bias device 100 is shown. The biasforce is intended to be sufficiently high to spread the attachmentpoints (e.g., processes of adjacent vertebrae) and restore normal discheight in all postures. For example, in normal standing posture, thebias force is sufficiently high to spread the attachment points as shownin FIG. 16, such that more normal disc size and shape is obtained. Asthe spine is placed in flexion and extension, the amount of forcecarried by the dynamic bias device 100 will change as a function of thespring properties, including the spring constant (K) and the compressionlength of the spring.

In a preferred embodiment, the bias force is sufficient to shift thepre-implant (normal posture) distance to the post-implant (normalposture) distance. To prevent excessive compression of the disc,particularly the posterior disc, it is also preferred that the biasforce increase significantly as the attachment points come closer, as byextension, lifting and/or poor posture. This is facilitated by thenatural increase in bias force of the spring as the distance decreases,and is aided by the damper pad and the compression limit (bottomed out)of the spring. In addition, because the dynamic bias device is intendedto limit excessive compression of the posterior disc, and notnecessarily intended to limit flexion of the spine, it is alsopreferable that the bias force approach zero (spring fully extended) ata distance which is less than the extension limit of the dynamic biasdevice.

Thus, by way of example, not limitation, the bias force may be in therange of 1% to 30% BW when laying down. With other postures afterimplantation, the bias force may be estimated by subtracting thecontribution of body weight from the load carried by lumbar region 12,which is approximately 50% BW (head=5% BW; arms=9% BW; trunk=36% BW). Assuch, the bias force may be in the range of 10% to 90% BW when standing.

With reference to FIGS. 4A-4B and 5A-5B, left lateral and posteriorviews of dynamic bias devices 100 are schematically illustrated as beingmounted to adjacent spinous processes 24 _(S) and 24 _(I) of adjacentvertebrae 20 _(S) and 20 _(I). When two or more dynamic bias devices 100are utilized per pair of vertebrae as shown in FIGS. 4A and 4B, thedynamic bias devices 100 are preferably mounted substantiallyequidistant from the median plane 70, or otherwise symmetric about themedian plane 70, in order to avoid causing lateral bias or curvature ofthe spine 10. Note that the dynamic bias devices 100 may be mountedsubstantially vertical as shown or at an angle to the median plane 70and satisfy these criteria. When only one dynamic bias device 100 isutilized per pair of vertebrae as shown in FIGS. 5A and 5B, the dynamicbias device 100 is preferably mounted in or near the median plane 70 forthe same reason.

Although it is preferable to have the dynamic bias device(s) 100 nearthe median plane 70, substantially equidistant from the median plane 70,or otherwise symmetric about the median plane 70, it is possible to havemultiple dynamic bias devices 100 mounted asymmetrically whilemaintaining balanced bias forces about the median plane 70. Theobjective is to avoid causing lateral bias or curvature of the spine 10,which is a function of balancing bias forces and moments about themedian plane 70.

The bias forces are vectors which have a magnitude governed by theproperties of the bias member 104, and a direction dictated by themounting position of the dynamic bias device 100. Each dynamic biasdevice 100 has two bias force vectors, one for each attachment member102 at each attachment point. Each bias force vector has a moment armequal to the distance from the attachment point to the median plane 70.For each attachment point, the product of the moment arm and thevertical component of the bias force vector is the moment or torqueapplied to the spine 10, and the horizontal component of the bias forcevector is the shear applied to the spine 10. Thus, in order to minimizecurvature of the spine 10, all of the moments are balanced about themedian plane 70. In order to minimize lateral bias on the spine 10, allof the horizontal components of the bias force vectors are balancedabout the median plane 70. The easiest way to accomplish this result, ofcourse, is to mount the dynamic bias devices 100 symmetrically about themedian plane 70. However, those skilled in the art will recognize thatasymmetric mounting arrangements that substantially meet these criteriaare also possible.

Further, because most protrusions 56 are posterior, the dynamic biasdevice(s) 100 is/are preferably mounted posterior to the axis ofcurvature 60. This is advantageous because loss of disc height is mostcommon in the posterior disc 50, the largest amount of mechanicaladvantage about the anterior disc is obtained posterior to the axis ofcurvature 60, and the posterior portions of the vertebrae are easiest toaccess less invasively. However, the dynamic bias device(s) 100 may bemounted at any position relative to the axis of curvature 60 dependingon the location of the protrusion 56, as long as the dynamic biasdevice(s) 100 is/are near the median plane 70, substantially equidistantfrom the median plane 70, or otherwise symmetric about the median plane70 as discussed above.

Given these criteria, there are many suitable mounting locations orattachment points for the dynamic bias device 100. Some of the possibleattachment points are labeled A-N in FIGS. 1A and 1B. Attachment pointsA-G refer to the lumbar vertebrae 20 (L1-L5), and attachment points H-Nrefer to the sacral vertebrae 30 (particularly S1). The attachmentpoints A-G of the lumbar region 12 are equally applicable to thethoracic and cervical regions of the spine 10, which are not illustratedfor purposes of simplicity only.

In the lumbar region 12, attachment points A and B refer to the leftlateral and right lateral surfaces of the spinous process 24; attachmentpoint C refers to the posterior surface of the spinous process 24;attachment points D and E refer to the posterior surfaces of the leftand right laminae 23; and attachment points F and G refer to the distalends of the left and right transverse processes 25.

In the sacrum 14, attachment points H and I refer to the left lateraland right lateral surfaces of the superior median sacral crest 31;attachment points K and L refer to the posterior surfaces of the sacrallaminae 33 between the median sacral crest 31 and the intermediatesacral crests 32; and attachment points M and N refer to posteriorsurface between the intermediate sacral crests 32 and the lateral sacralcrests 34.

A wide variety of sets of attachment points are possible, anon-exhaustive list of which is set forth herein. For single dynamicbias device 100 mounting, the nomenclature is (X₁Y₁) where X₁ is theattachment point on vertebra X, and Y₁ is the attachment point onvertebra Y. For double dynamic bias device 100 mounting, thenomenclature is (X₁Y₁, X₂Y₂) where X₁ is the attachment point of thefirst dynamic bias device 100 on vertebra X, Y₁ is the attachment pointof the first dynamic bias device 100 on vertebra Y, X₂ is the attachmentpoint of the second dynamic bias device 100 on vertebra X, and Y₂ is theattachment point of the second dynamic bias device 100 on vertebra Y.Vertebrae X and Y refer to any two different vertebrae, which areusually, but not necessarily, adjacent. In addition, vertebrae X and Ymay be superior and inferior, respectively, or vice-versa.

To illustrate the attachment point nomenclature, reference may be madeto FIGS. 4B and 5B. In FIG. 4B, a first dynamic bias device 100 isattached to the left lateral surface of the two spinous processes, and asecond dynamic bias device 100 is attached to the right lateral surfaceof the two spinous processes. Thus, the set of attachment points for thearrangement of FIG. 4B is (AA, BB). In FIG. 5B, only one dynamic biasdevice 100 is attached to the posterior surface of the two spinousprocesses. Thus, the set of attachment points for the arrangement ofFIG. 5B is (CC).

By way of example, not limitation, the following sets of attachmentpoints may be used to satisfy the above-referenced criteria with regardto balancing moments and forces about the median plane 70. For singledynamic bias device 100 mounting: (CC); and (CJ) are preferred. Fordouble dynamic bias device 100 mounting: (AA, BB); (DD, EE); (FF, GG);(AH, BI); (DK, EL); (FK, GL); (DM, EN); and (FM, GN) are preferred. Alsofor double dynamic bias device 100 mounting: (AD, BE); (AF, BG); (AK,BL); (AM, BN); (DH, El); (DF, EG); (FH, GI); (CA, CB); (CH, CI); (CD,CE); (CF, CG); (CK, CL); (CM, CN); (JA, JB); (JH, JI); (JD, JE); and(JF, JG) are possible. For more than double mounting, any combination ofthese sets may be used. Generally, the more posterior the attachmentpoints, the less invasive the procedure will be. Attachment points A, B,C, H and I are preferred for this reason. In addition, to avoidinterfering with the motion of the vertebrae, the dynamic bias device140 is preferably disposed laterally or posteriorly of the spinousprocesses 24, as opposed to under and between the spinous processes 24.

The dynamic bias device 100 may be attached to these points byconventional surgical techniques, except as described herein. Theposterior musculature and connective tissues may be dissected to exposethe desired attachment points. If desired, any disc protrusions 56 maybe removed, in whole or in part, using a conventional discectomyprocedure. Also if desired, any other abnormal spinal growths orprotrusions may be removed. However, for many disc protrusions 56, it isanticipated that conventional traction or separation techniques may beemployed to temporarily retract the protrusion 56 into the normal discspace until the dynamic bias devices are implanted.

In order to establish separation of the vertebrae, the spine may beplaced in traction or conventional intervertebral separation tools maybe used. Alternatively, the dynamic bias device 100 may be preloadedsuch that when the device is released after attachment, the bias forceestablishes the desired amount of separation.

Pilot holes are drilled as needed, such as for the use of bushings 330,340 and/or 350 (described with reference to FIGS. 7A-7B, 8A-8B and 9A-9Bhereinafter). If attachment points A, B, H and I are to be used, such aswith the use of bushing 320 (described with reference to FIGS. 6A-6Dhereinafter), a hole 90 and counter-bore 92 may be drilled into thespinous process 24. The device(s) 100 are then attached to the desiredattachment points in accordance with the hardware being used, and thesite is subsequently surgically closed.

With reference to FIGS. 6A-6D, 7A-7B, 8A-8B and 9A-9B, variousembodiments of bushings 320, 330, 340, and 350, respectively, areillustrated. As mentioned previously, the attachment members 102 maycomprise a wide variety of mechanical connection designs, and mayincorporate into their design, or be used in combination with, othermachine elements such as bushings 320, 330, 340, and 350. Bushings 320,330, 340, and 350 are adapted to mount one or two dynamic bias devices100. As illustrated, bushings 320, 330, 340, and 350 are adapted toreceive attachment members 102 in the form of loops or the like, but maybe modified to receive other structures. A primary function of bushings320, 330, 340, and 350 is to isolate movement of the attachment members102 from the vertebrae to which they are attached. Thus, the bushing tobone (vertebrae) interface is static, while the bushing to attachmentmember interface is dynamic. This reduces if not eliminates the abrasivedegradation of the vertebrae due to the attachment of the dynamic biasdevice 100. The orientation of the vertebral surface at the attachmentpoints will determine the best bushing scheme.

With reference to FIGS. 6A-6B, end and exploded views, respectively, ofa bushing 320 are illustrated. Bushing 320 is particularly suitable forattachment to the spinous process 24 as shown in FIG. 6C, or attachmentpoints A, B, H and I as illustrated in FIG. 1A. Bushing 320 may beattached to the spinous process 24 utilizing a conventional fastener300, which includes bolt 302, nut 304 and washers 306 and 308.Preferably, the fastener 300 is a lock fastener such that it will nothave a tendency to unscrew with relative motion of the attachmentmembers 102. However, the nut 304 is not tightened so much as to inhibitrotational movement of the attachment members 102. Fastener 300 mayalternatively comprise a key and pin (e.g., cotter pin). When fullyassembled, the attachment members 102 are disposed around the shaft ofthe bolt 302 on either side of the bushing 320 and between the washers306 and 308.

Bushing 320 includes a male fitting 321 which fits into a female fitting324. The male fitting 321 includes a shank portion 322 and a headportion 323. Similarly, the female fitting 324 includes a shank portion325 and a head portion 326. The female fitting 324 has an insidediameter sized to accommodate the shank 322 of the male fitting 321, andthe male fitting 321 has an inside diameter sized to accommodate thebolt 302 of the fastener 300. The outside surface of the shank 322 ofthe male fitting 321 and the inside surface of the shank 325 of thefemale fitting 324 may include mating threads.

The size of the head 323/326 to bone interface is preferably maximizedto minimize stress concentration and to distribute torsional loads overa large surface area. The size of the female shank 25 and thecorresponding size of the hole 90 drilled through the spinous process 24are chosen to minimize stress concentration and minimize the loss ofbone integrity. A counter-bore 92 may be used to flatten and therebymaximize the contact surface area of the head 323/326 to bone interface,as illustrated in FIG. 6D.

The materials of the fastener 300 and bushing 320 may comprise anysuitable implantable material capable of withstanding high fatigue. Forexample, all components could be comprised of 300 or 400 seriesstainless steel, titanium alloy 6-4, or MP35N alloy. Preferably, allcomponents would be made of the same or similar material to reducegalvanic corrosion. The surfaces of the fastener 300 and bushing 320that engage the attachment members 102 of the dynamic bias device 100are preferably smooth to reduce friction and wear. The surfaces of thebushing 320 that engage the vertebrae may have a roughened surface(e.g., knurled) to reduce the likelihood of relative movement therebetween. In addition, the surfaces of the bushing 320 that engage thevertebrae may have a porous sintered surface to facilitate solid bonegrowth, thereby further securing the bushing 320. Coatings and surfacetreatments may be utilized to reduce or increase friction where desired,and biological response where tissue interface is likely.

With reference to FIGS. 7A-7B, end and exploded views, respectively, ofa bushing 330 are illustrated. Except as described herein, bushing 330is substantially the same in design, function and use as bushing 320.Bushing 330 is adapted to mount one or (preferably) two dynamic biasdevices 100. Bushing 330 is particularly suitable for attachment pointsC and J as illustrated in FIG. 1B. Bushing 330 may be attached to thevertebrae 20/30 utilizing a conventional bone screw 310, which may bemodified in diameter, length and thread type for the particularattachment site and condition.

Bushing 330 includes two male fittings 331 which fit into a femalefitting 334. The male fittings 331 each include a shank portion 332 anda head portion 333. Similarly, the female fitting 334 includes two shankportions 335 and two head portions 336. The female fitting 334 has aninside diameter sized to accommodate the shanks 332 of the male fittings331, and the male fittings 331 have an inside diameter sized toaccommodate the bolt 302 of the fastener 300. The outside surfaces ofthe shanks 332 of the male fittings 331 and the inside surfaces of theshanks 335 of the female fitting 334 may include mating threads. Whenfully assembled, the attachment members 102 are disposed around theshanks 335 on either side of heads 336 of the female fitting 334 andbetween the heads 333 of the male fittings 331.

With reference to FIGS. 8A-8B, end and exploded views, respectively, ofa bushing 340 are illustrated. Except as described herein, bushing 340is substantially the same in design, function and use as bushing 330.Bushing 340 is adapted to mount one dynamic bias device 100. Bushing 340is particularly suitable for attachment points C, D, E, F, G, J, K, L, Mand N, but may also be used for attachment points A, B, H and I asillustrated in FIGS. 1A and 1B. Bushing 340 may be attached to thevertebrae 20/30 utilizing a conventional bone screw 310, which may bemodified in diameter, length and thread type for the particularattachment site and condition.

Bushing 340 includes a male fitting 341 which fits into a female fitting344. The male fitting 341 includes a shank portion 342 and a headportion 343. Similarly, the female fitting 344 includes a shank portion345 and a head portion 346. The female fitting 344 also includes aflange 347 connecting the bone screw 310 to the bushing 340. The femalefitting 344 has an inside diameter sized to accommodate the shank 342 ofthe male fitting 341, and the male fitting 341 has an inside diametersized to accommodate the bolt 302 of the fastener 300. The outsidesurface of the shank 342 of the male fitting 341 and the inside surfaceof the shank 345 of the female fitting 344 may include mating threads.When fully assembled, the attachment member 102 is disposed around theshank 345 on the female fitting 344 and between the heads 343/346 of thefittings 341/344. When mounted, the axis of the shank 345 of bushing 340is oriented parallel to the mounting surface.

With reference to FIGS. 9A-9B, end and exploded views, respectively, ofa bushing 350 are illustrated. Except as described herein, bushing 350is substantially the same in design, function and use as bushing 340.Bushing 350 is adapted to mount one dynamic bias device 100. Bushing 350is particularly suitable for attachment points C, D, E, F, G, J, K, L, Mand N, but may also be used for attachment points A, B, H and I asillustrated in FIGS. 1A and 1B. Bushing 350 may be attached to thevertebrae 20/30 utilizing a conventional bone screw 310, which may bemodified in diameter, length and thread type for the particularattachment site and condition. In this particular embodiment, thefastener 300 is formed integrally with the bone screw 310.

Bushing 350 includes a male fitting 351 which fits into a female fitting354. The male fitting 351 includes a shank portion 352 and a headportion 353. Similarly, the female fitting 354 includes a shank portion355 and a head portion 356. The female fitting 354 has an insidediameter sized to accommodate the shank 352 of the male fitting 351, andthe male fitting 351 has an inside diameter sized to accommodate thebolt 302, which is integral with the bone screw 310. The outside surfaceof the shank 352 of the male fitting 351 and the inside surface of theshank 355 of the female fitting 354 may include mating threads. Whenfully assembled, the attachment member 102 is disposed around the shank355 on the female fitting 354 and between the heads 353/356 of thefittings 351/354. When mounted, the axis of the shank 355 of bushing 350is oriented perpendicular to the mounting surface.

With reference to FIGS. 10A-10C, side views of a dynamic bias device 110are illustrated in a no-load condition, in a compression load condition,and in cross-section, respectively. Except as described herein, dynamicbias device 110 is substantially the same in design, function and use asthe generic device 100 described previously. Dynamic bias device 110includes a barrel 111 in which piston 112 is slidably disposed. A biasmember in the form of a spring 113 is disposed in the barrel 111.Longitudinal displacement of the barrel 111 relative to the piston 112causes compression (or extension) of the spring 113. The spring 113provides a bias force which increases (or decreases) linearly withdisplacement as discussed previously. A flexible housing (not shown) maybe placed about the dynamic bias device 110 to isolate the moving parts111/112 from the surrounding tissue when implanted.

An adjustable arm 114 may be connected to the piston 112. The arm 114and the barrel 111 include holes 115 or other suitable attachmentmembers, which may be used in combination bushings 320, 330, 340 and350, to attach the dynamic bias device 110 to the vertebrae. Theadjustable arm 114 and the piston 112 may include mating threads suchthat rotation of the arm 114 causes the arm 114 to effectively lengthenor shorten the piston 112. This allows the distance between the holes115 to be varied to accommodate different attachment locations anddifferent anatomies. This also allows the dynamic bias device to bepreloaded by extending the effective length of the piston 112 beyond thedistance between attachment points.

A collar 116 is provided to limit the extended length of the dynamicbias device 110. The collar 116 may include threads that mate withthreads inside the barrel 111 such that the collar 116 is adjustable,and thus the extended length is adjustable. The collar 116 may alsoinclude an elastomeric bumper pad to dampen impact between the piston112 and the collar when the device 110 is filly extended. Similarly, aelastomeric bumper pad 117 may be provided in the barrel 111 to dampenimpact between the piston 112 and the barrel 111 when the device 110 isfilly collapsed.

With reference to FIG. 11A, a cross-sectional view of a dynamic biasdevice 120 is illustrated. Except as described herein, dynamic biasdevice 120 is substantially the same in design, function and use asdynamic bias device 110 discussed with reference to FIGS. 10A-10C.Dynamic bias device 120 includes a barrel 121 in which piston 122 isslidably disposed. A bias member 123 in the form of a compressed orevacuated fluid (liquid or gas or a combination of both) is disposed inthe barrel 121 and sealed relative to the piston 122 by piston ring 128.The barrel 121 and piston 122 may define a closed volume or an exhaustreservoir 129 may be used as shown. The bias fluid 123 is in fluidcommunication with the exhaust reservoir 129 by way of an exhaust portthrough the wall of the barrel 121. The exhaust reservoir 129 maycomprise an expandable annular bag as shown, or other suitablestructure. If a closed volume is used, longitudinal displacement of thebarrel 121 relative to the piston 122 simply causes a change in pressureof the fluid 123. If an exhaust reservoir 129 is used as shown,longitudinal displacement of the barrel 121 relative to the piston 122causes a change in pressure of the fluid 123 and flow of fluid 123 intothe exhaust reservoir 129 via the exhaust port. The pressure of thefluid 123 and the size of the exhaust hole dictates the bias force whichincreases (or decreases) with the time derivative of displacement asdiscussed previously.

A flexible housing (not shown) may be placed about the dynamic biasdevice 130 to isolate the moving parts 121/122 from the surroundingtissue when implanted. The housing may be used to define the exhaustreservoir 129. An adjustable arm 124 may be connected to the piston 122.The arm 124 and the barrel 121 include holes 125 or other suitableattachment members to attach the dynamic bias device 120 to thevertebrae. The adjustable arm 124 and the piston 122 may include matingthreads to effectively lengthen or shorten the piston 122. An adjustablecollar 126 may be provided including mating threads such that the collar126 is adjustable, and thus the extended length of the dynamic biasdevice 120 is adjustable. The collar 126 may include an elastomericbumper pad (not shown) and an elastomeric bumper pad 127 may be providedin the barrel 121 to dampen impact between the piston 122 and the barrel121.

With reference to FIG. 11B, a cross-sectional view of a dynamic biasdevice 130 is illustrated. Except as described herein, dynamic biasdevice 130 is substantially the same in design, function and use as thecombination of dynamic bias device 110 discussed with reference to FIGS.10A-10C and dynamic bias device 120 described with reference to FIG.11A.

Dynamic bias device 130 includes a barrel 131 in which piston 132 isslidably disposed. A bias member is the form of a spring 133A isdisposed in the barrel 131. Longitudinal displacement of the barrel 131relative to the piston 132 causes compression (or extension) of thespring 133. The spring 133 provides a bias force which increases (ordecreases) linearly with displacement as discussed previously. Inaddition, a bias member 133B in the form of a compressed or evacuatedfluid (liquid or gas) is disposed in the barrel 131 and sealed relativeto the piston 132 by piston ring 138.

The barrel 131 and piston 132 may define a closed volume or an exhaustreservoir 129 may be used as shown. The bias fluid 133 is in fluidcommunication with the exhaust reservoir 139 by way of an exhaust portthrough the wall of the barrel 131. The exhaust reservoir 139 maycomprise an expandable annular bag as shown, or other suitablestructure. If a closed volume is used, longitudinal displacement of thebarrel 131 relative to the piston 132 simply causes a change in pressureof the fluid 133. If an exhaust reservoir 139 is used as shown,longitudinal displacement of the barrel 131 relative to the piston 132causes a change in pressure of the fluid 133 and flow of fluid 133 intothe exhaust reservoir 139 via the exhaust port. The pressure of thefluid 133 and the size of the exhaust hole dictates the bias force whichincreases (or decreases) with the time derivative of displacement asdiscussed previously. Thus, the bias members 133A/133B effectively actas a combined spring and damper.

A flexible housing (not shown) may be placed about the dynamic biasdevice 130 to isolate the moving parts 131/132 from the surroundingtissue when implanted. The housing may be used to define the exhaustreservoir 139. An adjustable arm 134 may be connected to the piston 132.The arm 134 and the barrel 131 include holes 135 or other suitableattachment members to attach the dynamic bias device 130 to thevertebrae. The adjustable arm 134 and the piston 132 may include matingthreads to effectively lengthen or shorten the piston 132. An adjustablecollar 136 may be provided including mating threads such that the collar136 is adjustable, and thus the extended length of the dynamic biasdevice 130 is adjustable. The collar 136 may include an elastomericbumper pad (not shown) and an elastomeric bumper pad 137 may be providedin the barrel 131 to dampen impact between the piston 132 and the barrel131.

With reference to FIGS. 12A-12B, rear and side views of dynamic biasdevice 140 are illustrated in no-load condition. FIG. 12C illustratesthe dynamic bias device 140 subjected to a compression load. Except asdescribed herein, dynamic bias device 140 is substantially the same indesign, function and use as the generic device 100 described previously.Although movement of the dynamic bias device 140 in compression andextension is substantially linear and parallel to the axis of curvature60, as with dynamic bias device 100, some lateral or posterior-anteriormotion is present, but preferably minimized. Dynamic bias device 140includes bias member 142 and loops 144 or other suitable attachmentmembers, which may be used in combination bushings 320, 330, 340 and350, to attach the dynamic bias device 140 to the vertebrae. The biasmember 142 is may be a semi-circular or semi-elliptical leaf spring,which may be a single plate as shown or a series of laminated plates.Relative longitudinal displacement of the attachment members 144 causescompression (or extension) of the leaf spring 142. The leaf spring 142provides a bias force which increases (or decreases) with displacementas discussed previously.

The radius or axis of curvature of the leaf spring 142 is preferablymaximized such that displacement of the attachment members 144 issubstantially linear, but should not be so high as to result in bucklingor inversion in compression. By way of example, not limitation, theradius or axis of curvature may range from half the distance between theattachment points to approximately 10 cm. Of course, half the distancebetween attachment points will vary depending on the location of eachattachment point, but will likely be in the range of 1.0 to 3.0 cm forattachment points between adjacent processes.

The displacement of the apex 143 is preferably of the leaf spring 142minimized to minimize disturbance of and interference from surroundingtissue (bone, muscle, connective tissue, nerves, etc.). The apex 143 mayface anteriorly, but preferably faces posteriorly or laterally to reduceinterference with tissue close to the spinal column. The dynamic biasdevice 140, and particularly the leaf spring 142, is preferably disposedlaterally or posteriorly of the spinous processes 24 to avoidinterference with movement of the vertebrae.

With reference to FIGS. 13A-13C, various alternative dynamic biasdevices 150, 160 and 170 are illustrated in side and posterior views.Except as described herein, dynamic bias devices 150, 160 and 170 aresubstantially the same in design, function and use as the dynamic biasdevice 140 discussed with reference to FIGS. 12A-12C.

Dynamic bias device 150 as seen in FIG. 13A includes bias member 152 inthe form of an articulated leaf spring, and attachment members 154.Articulated leaf spring 152 reduces the horizontal range of movement byutilizing a plurality of articulations 153 having a smaller radius oraxis of curvature. The reduced horizontal range of movement of the biasmember 152 reduces the amount of disturbance and interference fromsurrounding tissue (bone, muscle, connective tissue, nerves, etc.).

Dynamic bias device 160 as seen in FIG. 13B includes a plurality of biasmembers 162 in the form of leaf springs (shown) or articulated leafsprings (not shown), and attachment members 164. Utilizing a pluralityof leaf springs 162 increases stability of the dynamic bias device 160and allows for greater net bias forces to be delivered to the attachmentmembers 164 and the vertebrae attached thereto.

Dynamic bias device 170 as seen in FIG. 13C includes a plurality of biasmembers 172 in the form of leaf springs (shown) or articulated leafsprings (not shown). The dynamic bias device 170 also includesattachment members 174 in the form of inverted semi-circular loops. Theinverted semi-circular loops 174 permit the device 170 to be attached tothe inferior and superior sides spinous processes of adjacent vertebrae,such that the attachment members 174 are disposed between adjacentspinous processes but the bias members 172 are disposed laterally of thespinous processes to avoid interference with movement of the vertebrae.

Dynamic bias devices 110, 120, 130, 140, 150, 160 and 170 may be used(i.e., implanted) substantially as described with reference to genericdynamic bias device 100. As mentioned previously, one or morereinforcement members 200 may be used in combination with one or moredynamic bias devices 100. The reinforcement members 200 may be used toreinforce the disc, restore disc height and/or bear some or all of theload normally carried by the annulus. The reinforcement members 200 arerelatively rigid and thus serve to reinforce the disc 50, andparticularly the annulus 52, where inserted. In addition, thereinforcement members 200 may have a relatively large profile whenimplanted and thus increase disc height.

The reinforcing members 200 may be used singularly or in groups,depending on the increase in disc 50 height desired and/or the amount ofreinforcement of the annulus 52 desired. For example, the reinforcingmembers 200 may be stacked as illustrated in FIG. 2B or insertedside-by-side as illustrated in FIG. 15R. In addition, the reinforcingmembers 200 may be located in virtually any portion of the annulus 52.Preferably, the reinforcing members 200 are substantially symmetricallydisposed about the median plane 70 to avoid causing curvature of thespine 10. Although the reinforcing members 200 may be inserted, in partor in whole, into the nucleus 54, it is preferable to insert them intothe annulus 52 for purposes of stability and load carrying.Specifically, to provide stability, it is desirable to symmetricallylocate the reinforcing members 200 as far as reasonably possible fromthe median plane 70, or to span as great a distance as possible acrossthe median plane 70. In addition, because the annulus 52 of the disc 50is believed to carry the majority of the load, particularly in thelumbar region 12, the reinforcing members 200 are preferably placed inthe annulus 52 to assume the load normally carried thereby, andreinforce the load bearing capacity of the annulus 52, without hinderingthe normal mobility function of the disc 50.

The reinforcing members 200 may comprise expandable members such asself-expanding members 210 or inflatable members 220. Alternatively, thereinforcing members 200 may comprise unexpandable members such asreinforcement bars 230. When implanting each type of reinforcementmember 210/220/230, it is preferable to maintain the integrity of theannulus 52. Accordingly, space in the annulus 52 for the reinforcingmembers 200 is preferably established by dilation or the like, althoughsome amount of tissue removal may be used.

The expandable reinforcement members 210/220 are useful because they maybe delivered in a low profile, unexpanded condition making it easier totraverse the very tough and fibrous collagen tissue of the annulus 52.For similar reasons, the reinforcement bars 230 are useful because theymay have a small diameter and a sharpened tip. Although it is possibleto insert the expandable reinforcing members 210/220 into the annulus 52in their final expanded state, it is desirable to deliver the expandablereinforcing members 210/220 into the annulus 52 in an unexpanded stateand subsequently expand them in order to minimize invasiveness andresistance to insertion.

The self-expanding reinforcing member 210 may comprise a solid orsemi-solid member that self-expands (e.g., by hydration) after insertioninto the annulus. Examples of suitable materials for such solid orsemi-solid members include solid fibrous collagen or other suitable hardhydrophilic biocompatible material. If the selected material isdegradable, the material may induce the formation of fibrous scar tissuewhich is favorable. If non-degradable material is selected, the materialmust be rigid and bio-inert. The self-expanding reinforcing member 210preferably has an initial diameter that is minimized, but may be in therange of 25% to 75% of the final expanded diameter, which may be in therange of 0.3 to 0.75 cm, or 10% to 75% of the nominal disc height. Thelength of the self-expanding member 210 may be in the range of 1.0 to6.0 cm, and preferably in the range of 2.0 to 4.0 cm.

The inflatable reinforcing member 220 may comprise an expandable hollowmembrane capable of inflation after insertion into the annulus. Anexample of a suitable inflatable structure is detachable balloonmembrane filled with a curable material. The membrane may consist of abiocompatible and bio-inert polymer material, such as polyurethane,silicone, or polycarbonate-polyurethane (e.g., Corethane). The curablefiller material may consist of a curable silicone or polyurethane. Thefiller material may be curable by chemical reaction (e.g., moisture),photo-activation (e.g., UV light) or the like. The cure time ispreferably sufficiently long to enable activation just prior toinsertion (i.e., outside the body) and permit sufficient time fornavigation and positioning of the member 220 in the disc. However,activation may also take place inside the body after implantation. Theinflatable reinforcing member 220 preferably has an initial deflateddiameter that is minimized, but may be in the range of 25% to 75% of thefinal inflated diameter, which may be in the range of 0.3 to 0.75 cm, or10% to 75% of the nominal disc height. The length of the inflatablemember 220 may be in the range of 1.0 to 6.0 cm, and preferably in therange of 2.0 to 4.0 cm.

The reinforcement bars 230 may comprise a rigid, solid or hollow barhaving a sharpened tip. The reinforcement bars 230 may comprisesstainless steel mandrels, for example, having a diameter in the range of0.005 to 0.100 inches, preferably in the range of 0.010 to 0.050 inches,and most preferably in the range of 0.020 to 0.040 inches, and a lengthin the range of 1.0 to 6.0 cm, and preferably in the range of 2.0 to 4.0cm. The reinforcement bars 230 may be straight for linear insertion, orcurved to gently wrap with the curvature of the annulus duringinsertion. In addition, the outer surface of the reinforcement bars 230may have circular ridges or the like that the permit easy insertion intothe annulus 52 but resist withdrawal and motion in the annulus followingimplantation. Other suitable materials for reinforcement bars 230include titanium alloy 6-4, MP35N alloy, or super-elasticnickel-titanium alloy.

Referring now to FIGS. 14A-14D, various tools 410, 420 and 430 are shownindividually and assembled. The tools 410, 420 and 430 may be used toimplant the reinforcement devices 210/220/230 discussed above. The toolsinclude a rigid, sharpened, hollow needle 410, a semi-rigid, sharpened,hollow curved needle 420, and a sharpened stylet 430. As seen in FIG.14D, the sharpened stylet 430 fits into the semi-rigid needle 420 whichfits into the rigid needle 410.

With specific reference to FIG. 14A, the rigid hollow needle 410includes a hollow shaft 412 and a grip or handle 414. The shaft 412includes a sharpened tip 413 to facilitate insertion into and passthrough the surrounding tissue. The shaft 412 is preferably made of arigid metal such as a stainless steel hypodermic tube. The grip 414 maycomprise a polymer and may be formed by insert injection molding withthe shaft 412 inserted into the mold.

With specific reference to FIG. 14B, the semi-rigid curved needle 420includes a hollow shaft 422 a hub 424. The shaft 422, which includes asharpened tip 423, is longer than the rigid needle 410 and has anoutside diameter sufficiently small to fit into the rigid needle 410.The shaft 422 is preferably made of a semi-rigid polymer or composite.The shaft 422 includes a curved distal portion 426 that may bestraightened (shown in phantom) upon insertion of the semi-rigid needle420 into the lumen of the rigid needle 410. The hub 424 may include afitting 425 to facilitate connection to a fluid source or a pressuresource (e.g., a syringe).

With specific reference to FIG. 14C, the sharpened stylet 430 includes aflexible shaft 432 and a sharpened distal end 433. The shaft 432 islonger than the both the rigid needle 410 and the semi-rigid needle 420,and may have a length on the order of 10 to 60 cm. The shaft 432 alsohas an outside diameter sufficiently small to fit into the semi-rigidneedle 420. The shaft 422 preferably has a flexible but pushableconstruction incorporating a rigid metal such as stainless steel, orsuper-elastic nickel-titanium alloy. The sharpened stylet 430 ispreferably highly elastic, to resist permanent set upon insertion intothe curved portion 426 of the semi-rigid needle 420.

With general reference to FIGS. 15A-15J, the steps for implanting aself-expanding reinforcement member 210 are illustrated. It should beunderstood that the procedure for implanting a single member 210 in theanterior annulus 52 is shown for purposes of illustration, notlimitation. All of the variables with regard to quantity, location,orientation, etc. discussed previously may be implemented by varying thegeneric procedure described hereinafter.

Initially, the sharpened stylet 430, semi-rigid needle 420 and rigidneedle 410 are assembled as shown in FIG. 14D. As shown in FIG. 15A, thedistal portion of the assembly 410/420/430 is inserted into the disc 50as in a conventional discogram procedure. The assembly 410/420/430 isadvanced until the distal tip 413 of the rigid needle is proximate theanterior curvature of the annulus 52, near the anterior side of thenucleus 54, as seen in FIG. 15B. The semi-rigid needle 420 (alone orwith stylet 430) is advanced relative to the rigid needle 410 until thecurved portion 426 of the semi-rigid needle exits the distal tip 413 ofthe rigid needle 410 and the desired amount of curvature is established,as seen in FIG. 15C. The curved portion 426 may be advanced until thetip 423 is substantially parallel to the tangent of the anterior annulus52 curvature. The sharpened stylet 430 is advanced relative to thesemi-rigid needle 420 to the desired position within the anteriorannulus 52, as shown in FIG. 15D. The semi-rigid needle 420 and therigid needle 410 are completely withdrawn from the stylet 430, leavingthe stylet in position as shown in FIG. 15E.

A flexible dilator 440 is advanced over the stylet 430 to dilate theannulus 52, as seen in FIG. 15F. The flexible dilator 440 is similar tosemi-rigid needle 420 except that the dilator includes a blunt distaltip and is relatively more flexible, and has larger inner and outerdiameters. Note that one or more dilators 440 may be advanced co-axiallyabout the stylet 430 until the annulus is sufficiently dilated to acceptthe self-expandable member 210. The stylet 430 is then withdrawn fromthe flexible dilator 440 and the self-expandable member 210 isintroduced into the lumen of the flexible dilator 440 using a push bar450, as shown in FIG. 15G. Alternatively, the dilator 440 may be removedin favor of a flexible hollow catheter with a large inner diameter tofacilitate delivery of member 210. The push bar 450 is similar to stylet430 except that the distal tip of the push bar 450 is blunt.Alternatively, the push bar 450 may simply comprise the stylet 430turned around, thus using the proximal blunt end of the stylet 430 asthe push bar 450. The push bar 450 is advanced until the member 210 isin the desired position, as seen in FIG. 15H. To facilitate positioningthe member 210, radiographic visualization may be used to visualize thedistal end of the push bar 450, which is formed of radiopaque materialand may include radiopaque markers. In addition, the member may beloaded with a radiopaque material to facilitate radiographicvisualization thereof.

After the member 210 is in the desired position, the flexible dilator440 is retracted from the push bar 450 while maintaining position of themember 210 with the push bar. The push bar 450 is then removed leavingthe member 210 in place. If necessary, the procedure may be repeated foradditional member implants 210. The member 210 is then allowed to expandover time, perhaps augmented by placing the spine 10 in traction.Alternatively, the spine 10 may be placed in traction prior to beginningthe procedure as discussed with reference to the procedure forimplanting dynamic bias device 100.

With reference to FIGS. 15K-15L, the steps for implanting an inflatablereinforcement member 220 are illustrated. In this procedure, the stepsoutlined with reference to FIGS. 15A-15F are followed. Specifically, thesame steps are followed up to and including the step of advancing theflexible dilator 440 over the stylet 430 to dilate the annulus 52, andthereafter removing the stylet 430 from the flexible dilator 440. Usinga catheter 460, the inflatable member 220 is introduced into the dilator440 and advanced until the member 220 is in the desired position, asshown in FIG. 15K. The inflatable member 220 is connected to the distalend of the catheter 460, which includes a flexible but pushable shaft462 and an inflation port 464. The flexible dilator 440 is retractedfrom the catheter 460 while maintaining position of the member 220.

With the member 220 in the desired position, which may be confirmedusing radiographic visualization as described above, the proximalinflation port 464 is connected to a syringe (not shown) or othersuitable inflation apparatus for injection of the curable fillermaterial. The filler material is then activated and the desired volumeis injected into the catheter 460 via the inflation port 464, as seen ifFIG. 15L. The filler material is allowed to cure and the catheter 460 isgently torqued to break the catheter 460 from the solid member 220. Thisbreak-away step may be facilitated by an area of weakness at thejuncture between the distal end of the catheter 460 and the proximal endof the member 220. The catheter 460 is then removed leaving the member220 in place. If necessary, the procedure may be repeated for additionalmember implants 220.

With reference to FIGS. 15M-15R, the steps for implanting areinforcement bar 230 are illustrated. As seen in FIG. 15M, the disc 50includes a protrusion or bulge 56, which is preferably, but notnecessarily, reduced or eliminated before insertion of the reinforcementbar 230. This may be done by separating the adjacent vertebrae 20. Inorder to establish separation of the vertebrae 20, the spine 10 may beplaced in traction or conventional intervertebral separation tools maybe used. After the bulge 56 is reduced or eliminated, similar steps arefollowed as outlined with reference to FIGS. 15A-15C.

Delivery of a single reinforcement bar 230 into the posterior annulus 52is illustrated. Specifically, the distal portion of the assembly410/420/450 is inserted into the disc 50 as in a conventional discogramprocedure. The assembly 410/420/450 is advanced until the distal tip 413of the rigid needle 410 just penetrates the posterior side of theannulus 52, as seen in FIG. 15N. The semi-rigid needle 420 (alone orwith bar 230) is advanced relative to the rigid needle 410 until thecurved portion 426 of the semi-rigid needle 420 exits the distal tip 413of the rigid needle 410 and the desired amount of curvature isestablished, as shown in FIG. 15N. The curved portion 426 may beadvanced until the tip 423 is substantially parallel to the posteriorannulus 52.

Using the push bar 450, the reinforcement bar 230 with its sharpened tipis pushed into the annulus 52 as seen in FIG. 150. The reinforcement bar230 is advanced into the annulus 52 with the push bar 450 until the bar230 is in the desired position, as seen in FIG. 15P, which may beconfirmed using radiographic visualization as described above. The pushbar 450 is then retracted, leaving the reinforcement bar 230 in place,as shown in FIG. 15P. The semi-rigid needle 420 and the rigid needle 410are then removed, as shown in FIG. 15Q, or, if necessary, the proceduremay be repeated for additional reinforcement bar implants 230, as shownin FIG. 15R. Presence of the reinforcement bars 230 serves to keep thedisc 50, and particularly the bulge 56, in a more normal condition, andto protect against continued bulging, thus easing nerve impingement.

From the foregoing, those skilled in the art will appreciate that thepresent invention provides dynamic bias devices 100, 110, 120, 130, 140,150, 160, and 170, in addition to reinforcement devices 210, 220, and230, which may be used individually or in combination, to eliminatenerve impingement associated with a damaged disc 50, and/or to reinforcea damaged disc, while permitting relative movement of the vertebrae 20_(S) and 20 _(I) adjacent the damaged disc. The present invention alsoprovides minimally invasive methods of implanting such devices asdescribed above.

Those skilled in the art will recognize that the present invention maybe manifested in a variety of forms other than the specific embodimentsdescribed and contemplated herein. Accordingly, departures in form anddetail may be made without departing from the scope and spirit of thepresent invention as described in the appended claims.

1. A method of treating an intervertebral disc having an annulus and anucleus, comprising: providing a first elongate tubular member having aproximal end, a tissue penetrating distal end and a lumen extendingtherethrough; inserting the distal end of the first member into thedisc; providing a second elongate tubular member having a proximal end,a resiliently curved distal end and a lumen extending therethrough;inserting the second member into the lumen of the first member such thatthe distal end of the second member extends distally of the distal endof the first elongate member; and implanting a device in the disc via aninsertion path defined at least in part by the first and second elongatemembers.
 2. A method as in claim 1, wherein the implanted device isimplanted in the disc via the lumen of the second member.
 3. A method asin claim 1, wherein the implanted device is implanted in the annulus. 4.A method as in claim 1, wherein the implanted device is expandable.
 5. Amethod as in claim 4, wherein the implanted device is delivered in anunexpanded state.
 6. A method as in claim 5, wherein the implanteddevice is inflatable.
 7. A method as in claim 5, wherein the implanteddevice is self-expandable.
 8. A method as in claim 7, wherein theimplanted device expands by hydration.
 9. A method as in claim 8,wherein the implanted device comprises a hydrophilic material.
 10. Amethod as in claim 1, wherein the implanted device comprises a metallicmaterial.
 11. A method as in claim 10, wherein the implanted devicecomprises stainless steel.
 12. A method as in claim 10, wherein theimplanted device comprises a super-elastic alloy.
 13. A method as inclaim 10, wherein the implanted device comprises a nickel titaniumalloy.
 14. A method as in claim 10, wherein the implanted devicecomprises a MP35N alloy.
 15. A method as in clam 1, wherein the secondmember is inserted into the lumen of the first member such that thedistal end of the second member extends distally of the distal end ofthe first elongate member and points in a direction generally alignedwith an anterior or posterior curvature of the annulus.
 16. A method asin claim 1, wherein the distal end of the second member is configured topenetrate tissue.
 17. A method as in claim 16, wherein the second memberincludes a shaft portion and a sharpened distal tip.
 18. A method as inclaim 17, wherein the shaft potion of the second member comprises apolymer.
 19. A method as in claim 17, wherein the shaft portion of thesecond member comprises a composite.
 20. A method as in claim 1, whereinthe second member is longer than the first member.
 21. A method as inclaim 1, wherein the curved distal end of the second member straightensupon insertion into the first elongate member.
 22. A method as in claim21, wherein the first member comprises a rigid material.
 23. A method asin claim 22, wherein the first member comprises a metal.
 24. A method asin claim 22, further comprising: providing a third elongate memberhaving a proximal end and a distal end; and inserting the third memberinto the second member.
 25. A method as in claim 24, wherein the distalend of the third member extends beyond the distal end of the secondmember.
 26. A method as in claim 25, wherein the distal end of the thirdmember is configured to penetrate tissue, and wherein the tissuepenetrating distal end of the third member extends into disc tissue. 27.A method as in claim 26, wherein the third member includes a flexibleshaft portion and a sharpened distal tip.
 28. A method as in claim 24,wherein the third member comprises a push rod.
 29. A method as in claim28, wherein the implanted device is pushed out the distal end of thesecond member using the push rod.
 30. A method of treating anintervertebral disc having an annulus and a nucleus, comprising:providing a first elongate tubular member having a proximal end, atissue penetrating distal end and a lumen extending therethrough;inserting the distal end of the first member into the annulus; providinga second elongate tubular member having a proximal end, a curved tissuepenetrating distal end and a lumen extending therethrough; inserting thesecond member into the lumen of the first member such that the distalend of the second member extends distally of the distal end of the firstelongate member; and implanting a device in the disc via an insertionpath defined at least in part by the first and second elongate members.31. A method as in claim 30, wherein the implanted device is planted inthe disc via the lumen of the second member.
 32. A method as in claim30, wherein the implanted device is implanted in the annulus.
 33. Amethod as in claim 30, wherein the implanted device is expandable.
 34. Amethod as in claim 33, wherein the implanted device is delivered in anunexpanded state.
 35. A method as in claim 34, wherein the implanteddevice is inflatable.
 36. A method as in claim 34, wherein the implanteddevice is self-expandable.
 37. A method as in claim 36, wherein theimplanted device expands by hydration.
 38. A method as in claim 37,wherein the implanted device comprises a hydrophilic material.
 39. Amethod as in claim 30, wherein the implanted device comprises a metallicmaterial.
 40. A method as in claim 39, wherein the implanted devicecomprises stainless steel.
 41. A method as in claim 39, wherein theimplanted device comprises a super-elastic alloy.
 42. A method as inclaim 39, wherein the implanted device comprises a nickel titaniumalloy.
 43. A method as in claim 39, wherein the implanted devicecomprises a MP35N alloy.
 44. A method as in claim 30, wherein the secondmember is inserted into the lumen of the first member such that thedistal end of the second member extends distally of the distal end ofthe first elongate member and points in a direction generally alignedwith an anterior or posterior curvature of the annulus.
 45. A method asin claim 30, wherein the curved distal end of the second member isresilient.
 46. A method as in claim 45, wherein the curved distal end ofthe second member straightens upon insertion into the first elongatemember.
 47. A method as in claim 46, wherein the first member comprisesa rigid material.
 48. A method as in claim 47, wherein the first membercomprises a metal.
 49. A method as in claim 30, wherein the secondmember includes a shaft portion and a sharpened distal tip.
 50. A methodas in claim 49, wherein the shaft portion of the second member comprisesa polymer.
 51. A method as in claim 49, wherein the shaft portion of thesecond member comprises a composite.
 52. A method as in claim 30,wherein the second member is longer than the first member.
 53. A methodas in claim 30, further comprising: providing a third elongate memberhaving a proximal end and a distal end; and inserting the third memberinto the second member.
 54. A method as in claim 53, wherein the distalend of the third member extends beyond the distal end of the secondmember.
 55. A method as in claim 54, wherein the distal end of the thirdmember is configured to penetrate tissue, and wherein the tissuepenetrating distal end of the third member extends into disc tissue. 56.A method as in claim 55, wherein the third member includes a flexibleshaft portion and a sharpened distal tip.
 57. A method as in claim 53,wherein the third member comprises a push rod.
 58. A method as in claim57, wherein the implanted device is pushed out the distal end of thesecond member using the push rod.
 59. A method as in claim 58, whereinthe implanted device is self-expanding.
 60. A method of treating anintervertebral disc having an annulus and a nucleus, comprising:providing a tubular member having a proximal end, a distal end and alumen extending therethrough; inserting the distal end of the tubularmember into the disc; providing an elongate stylet having a proximal endand a tissue penetrating distal end; inserting the stylet through thetubular member and into the disc; providing a device having a lumenconfigured to accommodate the stylet; and advancing the device over thestylet and into the disc.
 61. A method as in claim 60, wherein thedistal end of the tubular member is curved.
 62. A method as in claim 61,wherein the curved distal end is resilient.
 63. A method as in claim 60,wherein the distal end of the tubular member is configured to penetratetissue.
 64. A method as in claim 63, wherein the distal end of thetubular member includes a sharpened tip.
 65. A method as in claim 60,wherein the stylet includes a flexible shaft portion.
 66. A method as inclaim 65, wherein the flexible shaft portion comprises a metallicmaterial.
 67. A method as in claim 66, wherein the metallic materialcomprises stainless steel.
 68. A method as in claim 66, wherein themetallic material comprises a nickel titanium alloy.
 69. A method as inclaim 66, wherein the metallic material comprises a MP35N alloy.
 70. Amethod as in claim 60, wherein the stylet has a length of about 10 cm to60 cm.